Google has quietly shut down a search function that helped users in China navigate past the country's censorship systems, after authorities had tried to block the feature.

Launched at the end of May, the function worked by highlighting terms that would likely result in a page error caused by China's censorship systems, known for filtering out sensitive and anti-government internet content.

But between Dec. 5 and Dec. 8, Google decided to remove the function, according to Greatfire.org, a site that monitors China's online censorship. Google spokesman Taj Meadows confirmed the function's shutdown, but the company declined to specify why.

The internet giant had originally hoped the function would improve the search experience for users in mainland China by reducing the chance of page errors. Google reviewed the 350,000 most popular search queries in China, and identified which search terms would likely trigger the errors. To use the function, users simply would type their query into Google's search bar, only to be warned if there was a likelihood their search would be blocked.

China's censorship systems, however, tried to block the function, only for Google to later embed it further into the search page, said Greatfire.org in a blog post. This made it impossible to block the function without blocking the Google site itself.

Greatfire.org criticized the function's shutdown as a "grave setback" in the fight against China's online censorship. Search engines that operate within China must adhere to the country's strict rules on online censorship. But in 2010, Google said it would no longer filter its search results for the country and shut down its China-based search engine at Google.cn. Now users in the country are redirected to Google's Hong Kong search engine, which offers unfiltered search results, but is still a target of Chinese censors.

Since Google closed its China-based search engine, the company's market share has fallen to about 5 percent in the country, according to data analytics sites CNZZ.com. Analysts point to constant page errors from blocked searches as a major reason for the decline.

Access to Google services in China continues to be slow and sometimes briefly inaccessible, which is likely caused by the country's censors. In November, all Google services were abruptly blocked for 12 hours in China.